Here, We see Validate Binary Search Tree LeetCode Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python, etc. with different approaches.

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Validate Binary Search Tree LeetCode Solution

Problem Statement

Given the root of a binary tree, determine if it is a valid binary search tree (BST).

A valid BST is defined as follows:

• The left subtree of a node contains only nodes with keys less than the node’s key.
• The right subtree of a node contains only nodes with keys greater than the node’s key.
• Both the left and right subtrees must also be binary search trees.

Example 1:

Input: root = [2,1,3]
Output: true

Example 2:

Input: root = [5,1,4,null,null,3,6]
Output: false
Explanation: The root node's value is 5 but its right child's value is 4.

Validate Binary Search Tree Leetcode Solution C++

class Solution {
public:
    bool isValidBST(TreeNode* root) {
        if(!root) return true;
        if(!isValid(root->left, root->val, true) || !isValid(root->right, root->val, false)) return false;
        return isValidBST(root->left) && isValidBST(root->right);
    }
    
    bool isValid(TreeNode* root, int bound, bool isLeft){
        return !root || (isLeft ? root->val < bound : root->val > bound ) && isValid(root->left, bound, isLeft) && isValid(root->right, bound, isLeft);
    }
};Code language: PHP (php)

Validate Binary Search Tree Leetcode Solution Java

class Solution {
    public boolean isValidBST(TreeNode root) {
        return isValidBST(root, Long.MIN_VALUE, Long.MAX_VALUE);
    }
    
    public boolean isValidBST(TreeNode root, long minVal, long maxVal) {
        if (root == null) return true;
        if (root.val >= maxVal || root.val <= minVal) return false;
        return isValidBST(root.left, minVal, root.val) && isValidBST(root.right, root.val, maxVal);        
    }
}Code language: PHP (php)

Validate Binary Search Tree Leetcode Solution JavaScript

var isValidBST = function(root) {
    function inOrder(node) {
        if(!node) return [];
        return [...inOrder(node.left), node.val, ...inOrder(node.right)]
    }
    
    const sortedArr = inOrder(root);
    
    for(let i = 0; i < sortedArr.length; i++) {
        if(sortedArr[i+1] <= sortedArr[i]) return false;
    }
    return true;    
};Code language: JavaScript (javascript)

Validate Binary Search Tree Leetcode Solution Python

class Solution(object):
    def isValidBST(self, root):
        stack = [None]
        prev = -float("inf")
        while stack:
            while root:
                stack.append(root)
                root = root.left
            x = stack.pop()
            if x:
                if x.val <= prev:
                    return False
                prev = x.val
                root = x.right
                
        return TrueCode language: HTML, XML (xml)